Demonstration of Steganography

This is an original image of aortic dissection.
The second, visually indistinguishable image contains a hidden file
called dissection.html. It was encrypted with the
S-Tools
program using the IDEA encryption algorithm with the file name:
"dissection.html" as the pass phrase needed to decrypt the hidden file.

Public Key Cryptography

Pretty Good Privacy (PGP)
is the encryption program that allows public key cryptography. Among
other things, echocardiographic images can be encrypted and sent
using e-mail. This is called ascii armor. It takes some reading and
thinking to understand the concepts of public and private keys and digital
signatures. This is a link to frequently asked questions about PGP.